Vapor or steam generating plant with resuperheaters



Aug. 26, 1958 A. LIEBERHERR 2,848,983

VAPOR 0R STEAM GENERATING PLANT WITH RESUPERHEATERS Filed Dec. 20, 1954INVENTOR. A RTHUE L 1 EBEEHERE.

m romvfx United States Patent 1C@ VAPOR R STEAM GENERATING PLANT WITHRESUPERHEATERS Arthur Lieberherr, Winterthur, Switzerland, assignor toSulzer Freres, Societe Anonyrne, Winterthur, Switzerland, a corporationof Switzerland Application December 20, 1954, Serial No. 476,189

Claims priority, application Switzerland December 23, 1953 4 Claims.(Cl. 122-479) The present invention relates to a vapor generating powerplant including resuperheating means interposed between the highpressure and the low pressure part of a turbine plant, theresuperheating means comprising a resuperheater heated by the combustionof fuel and a resuperheater heated by a medium which has been heated bythe combustion of fuel, the second resuperheater being arranged upstreamof the first-mentioned resuperheater. The indirectly heated secondresuperheater is used for controlling the temperature of theresuperheated vapor.

The vapor power plant according to the invention includes a forced flowvapor generator which is provided with two superheaters arranged inseries with respect to the vapor flow, the indirectly heatedresuperheater mentioned in the paragraph next above being interposedbetween the two superheaters for receiving heating vapor from onesuperheater and discharging the cooled heating vapor into the othersuperheater. The arrangement according to the invention affordsconvenient regulation of the temperature of the resuperheated steam inmodern steam power plants which are equipped with a forced flow steamgenerator and are operated at subcritical or supercritical pressure.

It has been proposed to arrange a steam heated regulating resuperheaterupstream of a combustion gas heated resuperheater with respect to theflow of the steam to be resuperheated. In such plants, wet steam istaken from the upper drum of a natural circulation boiler and used forheating the regulating resuperheater. The wet steam condenses and thecondensate flows by gravity from the regulating resuperheater back intothe upper boiler drum. Such an arrangement cannot be used in modernsteam power plants. The steam entering the regulating resuperheater hasa temperature which is far above the condensation temperature of the wetsteam, so that there is no heating but a cooling of the steam to beresuperheated, and there is no condensation of wet steam. Condensationis needed in the aforementioned conventional arrangement becauseotherwise a circulating pump must be provided to return the heatingsteam to the tube system of the steam generator.

The aforesaid difliculties are avoided,- if the regulating resuperheateris interposed in the steam flow between two superheaters to receiveheating steam from one superheater and to discharge it into the othersuperheater. The operating medium may be so much superheated in thefirst ofthe two superheaters, that its temperature is sufliciently highto heat the steam to be resuperheated. Since the entire amount of thesteam produced in the steam generator is available as heating steam, alarge amount of heat can be transferred to the steam to beresuperheated. Because the primary side of the regulating resuperheateris arranged in series with the superheaters of the steam generator, nocirculating pump is required.

There are many possibilities for regulating the temperature of the steamto be resuperheated by means of 2,848,983 Patented Aug. 26, 158

the regulating resuperheater. Of particular advantage is an arrangementin which water is injected into the tube system of the steam generatorupstream of the regulating resuperheater for controlling the temperatureof the heating steam. The water injection can be actuated automaticallyor by hand. A preferable arrangement includes a conduit through whichheating steam by-passes the regulating resuperheater, and a regulatingvalve in this conduit. As a modification, a by-pass conduit may beprovided, through which a portion of the steam to be resuperheatedby-passes the regulating resuperheater, a regulating valve beingprovided in the bypass conduit for the steam to be resuperheated.

The system according to the invention has many advantages. The heatingsteam for the regulating resuperheater can be taken from the tube systemof the steam generator at a point at which the steam temperature affordsconstruction of the regulating resuperheater of ferritic steel. Theresuperheating means, which include a steam heated resuperheater and acombustion gas heated resuperheater, can be so constructed that thetemperatures in the former afford construction of the steam heatedresuperheater of more or less highly alloyed ferritic steel, and onlythe combustion gas resuperheater need be made of considerably moreexpensive heat resisting steel, for example, austenitic steel. In thiscase, the heating steam would be taken from a point of the steamgenerator tube system at which the steam temperature is not more than550, depending on the degree of alloying of the ferritic steel. Theresuperheater can be further simplified by constructing the steam heatedsuperheater of low alloyed steel. Low alloyed steel contains not morethan 0.5% molybdenum and small traces of chromium, and need only beheated for stress-relieving anneal at circa 650-700 C., but not fornormalising at higher temperatures. Though the temperature of theheating steam must be below 500 C., if low alloyed ferritic steel isused for constructing the indirectly heated resuperheater, the requiredhigh resuperheat temperature can "be obtained without difiiculty bymeans of the combustion gas heated resuperheater which need not be verylarge even if it is arranged in the part of the steam generator which isshielded from radiant heat. The combustion gas heated resuperheater maybe placed, for example, in the boiler flue, i. e. in a zone in which thetemperature of the combustion gases is relatively low. In this manner,the directly gas heated resuperheater is well protected, without specialcooling arrangements, also during starting of the generator and at lowloadsv No provisions are needed for protecting the gas heatedresuperheaters as they are required in conventional arrangements.

The invention is not limited to plants having only one resuperheatingmeans. If the plant has two directly heated resuperheaters, a steamheated regulating resuperheater may be arranged upstream of at least oneof the directly heated resuperheaters. The second directly heatedresuperheater may be controlled, for example, by a swinging burner, ormay also be controlled by means of an indirectly heated regulatingresuperheater arranged upstream of the second gas heated resuperheater.

In the present specification and in the claims, the words vapor andsteam are used for indicating the gaseousv phase of the operatingmedium. The invention is applicable to plants using steam from water aswell as vapor from liquids other than water.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself however and additional objects and advantages thereof will bestbe understood from the following description of embodiments thereof whenread in conjunction with the accompanying drawing, in which Fig. 1 is adiagram of a plant according to the invention;

Fig; 2 diagrammatically shows a modified part of the plant according toFig. 1;

Fig. 3 diagrammatically illustrates a further modificationof a part ofthe plant shown in Fig. 1.

The same numerals designate the same parts in all figures.

Referring more particularly to the drawing, the operating medium isdrawn from a condenser 1 by means of a'condensate pump 2 and isconducted through a conduit 3 into a feed Water reservoir 4. A feed pump5 pumps water from the reservoir 4 and raises the pressure: of 'thewater to' the highest pressure of the plant. The feed waterisconductedthrough a conduit 6 into a first'heater 7 which is heated bycombustion gas produced by burning fuel in a device 32 and is generallyknown as an economizer. The preheated water enters a second heater 8which is adjacent to the fuel burning means 32 and exposed to radiantheat and in which the water. is converted into primary steam, which isconducted through a pipe 9 into a third heater 10 which is alsoheated bythe products of combustion produced by the fuel burning means 32 andwhich serves as primary or first superheater. At least a portion of theheater 10 isv exposed to radiant heat produced by the fuel burningmeans. The steam superheated in the first, relatively small superheater10 is conducted through a conduit 11 into the primary side of a heatexchanger serving as an indirectly heated regulating heat exchanger 12.The heating steam leaves the heat exchanger 12 through a conduit 13 andis once more superheated by products of combustion in a secondsuperheater 14, which supplies primary steam through a conduit 15 to thehigh pressure part 16 of a turbine plant. The secondary steam exhaustingfrom the turbine 16 is conducted through a conduit 17 into the secondaryside of the indirectly heated regulating resuperheater or heat exchanger12 from which the resuperheated steam is conducted into a combustion gasheated resuperheater 18. The steam, which now has the desiredresuperheat temperature, is conducted through a conduit 19 to the lowpressure stage 20 of the turbine plant. The steam exhausting from theturbine plant is conducted through a conduit 21 into the condenser 1.The high pressure part 16 and the low pressure part 20 of the turbineplant have a common shaft driving an electric generator 22.

There are several possibilities for regulating the heat exchanger 12. Itis of particular advantage to divert some water from the feed line 6through a conduit 23 and to inject the diverted water into the pipe 9downstream of the heater or evaporator 8, the amount of injected waterbeing controlled by a valve 24. The latter is actuated by a conventionaldevice 25. This device is actuated by a thermostat 26 which responds tothe temperature of the medium flowing through the pipe 9 after water hasbeen injected thereinto. The device 25 also responds to a thermostat 27which is actuated by thetemperature of the resuperheated steamdownstream of the directly heated resuperheater 18.

If, for example, the temperature of the steam resuperheated in theresuperheater 18 drops, the thermostat 27 actuates the device 25 andthereby the valve 24 in such manner that less water is injected into theconduit 9. Consequently, the operating medium is more heated inthesuperheater 10 and can transmit more heat to the steam to beresuperheated and increase its temperature. The valve 24 is opened ifthe temperature acting on thethermostat 27 increases. The thermostat 26is primarily for the purpose of stabilizing the water in jectioncontrol. Whereas the thermostat 27 indicates the-efie'ct of a change ofthe amount of injected water 4 and actuates the device 25 only after acertain lapse of time, the thermostat 26 responds immediately to theeffect of a change of the amount of injected water and will delay orlimit the actuation of the valve 24, thus preventing overregulation.

Since the indirectly heated resuperheater 12 is preferably made offerritic steel, particularly of low-alloyed ferritic steel, and is ofwelded construction, the heating surfaces of the superheaters 10 and 14will be so chosen that the temperature of the steam leaving thesuperheater 10 is below, for example, 500 C. at normal load conditions.

Fig. 2 shows a modified arrangement for controlling the regulatingresuperheater 12. A by-pass conduit 28 connects the conduits 11 and 13which are connected with the primary side of the regulatingresuperheater 12, a valve 29 being provided in the by-pass conduit 28,which valve is controlled according to the temperature measured by thethermostat 27. If the temperature of the resuperheated steam increases,the valve 29 is opened, so that a greater portion of the high pressureheating steam by-passes the resuperheater 12, reducing the amount ofheating steam flowing through the resuperheater and consequentlyreducing the temperature of the resuperheated steam. The valve 29 isclosed if the temperature of the resuperheated steam decreases.

A third modification of the control of the regulating resuperheater 12is illustrated in Fig. 3. The steam to be resuperheated can be by-passedthrough a conduit 30 around the secondary part of the resuperheater 12.A valve 31 arranged in the by-pas's conduit 30 is controlled accordingto the temperature measured by the thermostat 27. The valve 31 is openedif the temperature of the resuperheated steam increases, and a portionof the steam to be resuperheated flows into the gas heated resuperheater18 without prior heating in the regulating resuperheater 12, so that thetemperature of the total amount of steam at the outlet of theresuperheater 18 is reduced. The valve 31 is closed when the temperatureof the resuperheated steam drops.

The plants illustrated in the drawing may be modified in various wayswithout departing from the scope of the present invention. The turbineplant may consist of more than two parts, and consequently more than oneresuperheater may be provided. The additional resuperheaters, too, maybe controlled by the provision of a regulating resuperheater combinedaccording to the invention with a gas heated superheater. The inventionis not limited to plants having a forced flow steam generator, but canbe applied to plants having other types of conventional steam boilers.

What is claimed is:

1. In a vapor generating plant operating under the reheat cycle andunder variable load conditions, a forced flow vapor generator comprisingfuel burning means generating radiant heat and combustion gases, a firstrelatively small superheater exposed to radiant heat from said fuelburning means and a second superheater exposed to the combustion gasesfor superheating primary vapor, a resuperheater exposed to saidcombustion gases for resuperheating secondary vapor, a heat exchangerfor indirectly exchanging heat between the primary vapor and thesecondary vapor, said heat exchanger including a conduit interposedbetween said first and second superheater for conducting primary vaporas a heating medium from said first superheater through said heatexchanger to said second superheater, said heat exchanger including acompartment accommodating said conduit and having an inlet for receivingsecondary vapor which is to be resuperheated and having an outletconnected with said resuperheater for conducting partially resuperheatedsecondary vapor from said compartment into said resuperheater, an inletpipe connected with said first superheater, injecting means connectedwith said inlet pipe for injecting liquid into the primary vaporentering said first superheater for lowering the temperature of thesuperheated primary vapor entering said heat exchanger for controllingthe heat exchanged in said heat exchanger between the primary vapor andthe secondary vapor and for simultaneously protecting said superheateragainst overheating by the radiant heat.

2. In a vapor generating plant according to claim 1 temperatureresponsive means connected with said inlet pipe between the connectionof said injecting means with said inlet pipe and said first superheater,said temperature responsive means being connected with said injectingmeans for increasing the amount of liquid injected into said inlet pipewhen the temperature of the primary vapor entering siad firstsuperheater exceeds a predetermined value.

3. In a vapor generating plant according to claim 1 temperatureresponsive means connected with the outlet of said resuperheter andconnected with said injecting means for decreasing the amount of liquidinjected into said inlet pipe when the temperature of the secondaryvapor leaving said resuperheater falls below a predetermined value.

4. In a vapor generating plant operating under the reheat cycle andunder variable load conditions, a forced flow vapor generator comprisingfuel burning means generating products of combusiton, a first and secondsuperheater exposed to said products for superheating primary vapor, aresuperheater exposed to said products for resuperheating secondaryvapor, a heat exchanger for indirectly exchanging heat between theprimary vapor and the secondary vapor, said heat exchanger including aconduit interposed between said first and second superheater forconducting primary vapor as a heating medium from said first superheaterthrough said heat exchanger to said second superheater, said heatexchanger including a compartment accommodating said conduit and havingan inlet for receiving secondary vapor which is to be resuperheated andhaving an outlet connected with said resuperheater for conductingpartially resuperheated secondary vapor from said compartment into saidresuperheater, an inlet pipe connected with said first superheater,injecting means connected with said inlet pipe for injecting liquid intothe primary vapor entering said first superheater for lowering thetemperature of the superheated primary vapor entering said heatexchanger for controlling the heat exchanged in said heat exchangerbetween the primary vapor and the secondary vapor, first temperatureresponsive means connected with the outlet of said resuperheater andconnected with said injecting means for decreasing the amount of liquidinjected into said inlet pipe when the temperature of the secondaryvapor leaving said resuperheater falls below a below a predeterminedvalue, and second temperature responsive means connected with said inletpipe downstream of the connection of said injecting means with saidinlet pipe and connected with said injecting means for increasing theamount of liquid injected into said inlet pipe when the temperature ofthe primary vapor entering said first superheater exceeds apredetermined value.

References Cited in the file of this patent UNITED STATES PATENTS1,931,948 Armacost Oct. 24, 1933 2,579,027 Walter et a1. Dec. 18, 19512,602,433 Kuppenheimer July 8, 1952 2,649,079 Van Brunt Aug. 18, 19532,685,280 Blaskowski Aug. 3, 1954 FOREIGN PATENTS 581,458 Great BritainOct. 14, 1946

